PRTN3 and rheumatoid arthritis: Despite B cell lineage synovial and systemic signatures predominating in patients with positive autoantibodies, particularly ACPA [130,131,132,133,135], autoantibody-negative RA can still display features indicative of adaptive immune responses at the site of inflammation in a variable but significant proportion of the cases [130,131,133,137] (Table 1) and, at least in long-standing disease, B cell-rich synovitis can be detected in as many as 45% of patients, without significant differences compared with autoantibody-positive RA [135].